1. Field of the Invention
The present invention relates to an improvement of an electromagnetic induction heating device making use of an electromagnetic induction heating and an image recording device using such a heating device.
2. Related Art
Conventionally, as an image forming device such as a copying machine, a laser beam printer, a facsimile, a microfilm reader printer, an image display device or an electrostatic recording device or the like, an image forming device which forms an image by following steps has been known. That is, a sensible image (an unfixed toner image) corresponding to target image information is formed on a surface of a recording member (an electronic-fax sheet, an electrostatic recording sheet, a transfer material sheet, a printing sheet or the like) in a direct method or an indirect (transfer) method using a toner made of heat-soluble resin or the like by a suitable image forming processing unit such as an electrophotography, an electrostatic recording, a magnetic recording or the like. Then, this recording member is guided and conveyed to a heating and fixing device (an image heating device) where a heating and fixing processing is performed to form the above-mentioned image as a permanently fixed image on a surface of the recording member.
As such a heating and fixing device (image heating device), a device which adopts a heat roller system or a film heating system has been widely used.
The heat roll system includes a basic constitution which includes, for example, a metal-made heating and fixing roller incorporating a heater therein and a pressure fixing roller having resiliency which is brought into pressure contact with the heating and fixing roller. By delivering the recording member in a fixing nip area defined by a pair of these fixing rollers, a toner image is fixed by heating and pressing.
In such a heat roller system, since the heat capacity of the fixing rollers is large, it takes a considerably long time to elevate the temperature of surfaces of the fixing rollers to a fixing temperature and hence, it necessitates a long warmup. Further, to shorten time necessary for delivering the first printing, it has been necessary to prepare a standby state so as to always place the fixing rollers in a heated state.
These days, however, to overcome such a problem, efforts have been made to lower the heat capacity of the fixing roller as much as possible and now have realized a level which can eliminate the standby state.
On the other hand, as the film heating system, a device includes, in its constitution, a heater as a heating body fixedly supported, a heat-resistant film which is conveyed while being brought into pressure contact with the heater in an opposed manner and a pressure applying member which makes an object to be heated come into close contact with the heater by way of the heat-resistant film and transmits the heat of the heater to the recording member by way of the heat-resistant film.
This film heating system is a device which adopts following steps as its basic constitution. That is, the heat-resistant film is made to travel in the normal direction at the same speed as the recording member on which an image is to be fixed and which is delivered between the heat-resistant film and the pressure member. Then, by making the recording member pass through a fixing nip area formed by a pressure contact of the heat-resistant film and the pressuring member, a sensible image carrying surface of the recording member is heated by the heater by way of the heat-resistant film so as to apply heat energy to the sensible image of the recording member thus softening or fusing the sensible image. Subsequently, after passing through the fixing nip area, the heat-resistant film and the recording member are separated at a separation point.
In these heat roller system and film heating system, as the pressure/fixing roller or the pressure member, a roller body made of silicone rubber or fluororubber which exhibits excellent heat resistance and mold release characteristics has been widely used in general.
Further, as the heater, a halogen lamp or a thermal heater of the low heat capacity has been used.
The heating and fixing device adopting such a heat roller system or a film heating system has suffered from following technical problems.
That is, when a roller or a film having a large thickness and hence having high rigidity is used in consideration of the durability, the high-speed processing or the like, the heat conduction is deteriorated or the heat capacity is increased so that the thermal response is lowered whereby the state which allows the rapid heating cannot be achieved.
In other words, the roller or the film having a large thickness becomes a thermal resistance and may deteriorate the heat transfer from the heater to the recording member which constitutes the object to be heated and hence, it becomes difficult to save energy and to realize the quick starting.
To solve these technical problems, inventors of the present application have extensively studied an electromagnetic induction heating device making use of the electromagnetic induction heating which can improve the thermal efficiency by making the roller per se or the film per se generate heat thus preventing the roller or the film from becoming the heat resistance.
In such an electromagnetic induction heating device, a magnetic field generated by a magnetic field generating unit which may be formed by combining a core made of magnetic material and an exciting coil, for example, is changed by an exciting circuit (for example, a circuit which applies high-frequency wave to the exciting coil) and a roller or a film which includes an electromagnetic induction heat generating layer (conductive member xe2x80x9cinduction magnetic material, magnetic field absorption conductive materialxe2x80x9d) and constitutes an object to be heated is made to pass through the generated magnetic field, and an eddy current is generated in the electromagnetic induction heat generating layer of the roller or the film due to the repetition of the generation and the extinction of the magnetic field (a fluctuation magnetic field).
In such a mode, the eddy current is transferred to heat (Joule heat) by the electric resistance of the electromagnetic induction heat generating layer and eventually only the roller or the film which is brought into close contact with the recording member which constitutes the object to be heated generates heat and hence, it becomes possible to provide a heating device capable of exhibiting the excellent thermal efficiency.
That is, when the fluctuating magnetic field traverses the inside of the conductive body (the electromagnetic induction heat generating layer in the roller or the film), the eddy current is generated in the electromagnetic induction heat generating layer of the roller or the film so as to generate a magnetic field which prevents the change of the magnetic field. Due to the skin resistance of the electromagnetic induction heat generating layer of the roller or the film, this eddy current makes the electromagnetic induction heat generating layer of the roller or the film generate heat proportional to the skin resistance.
Here, when the electromagnetic induction heat generating layer is formed close to a surface layer of the roller or the film, it becomes possible to make a portion of the roller or the film close to a surface layer directly generate heat and hence, an advantage that object to be heated can be rapidly heated irrespective of the thermal conductivity and the heat capacity of the roller or the base layer of the film.
Accordingly, it becomes possible to make the roller or the film base layer have a large thickness which ensures the high rigidity without damaging the energy saving and the quick start characteristics so that the roller or the film can satisfy the demand for high durability and the high-speed processing.
However, such an electromagnetic induction heating device still has following technical problems.
1) Since an elongated core around which an exciting coil is wound is formed by an integral molding, it is difficult to adjust a heat value in a longitudinal direction.
2) Although the exciting coil wound around the elongated core has a pattern that the exciting coils are folded at both longitudinal ends thereof, an abnormal heating phenomenon occurs at both-end folding portions of the exciting coil due to the concentration of a magnetic field. Accordingly, the temperature distribution in the longitudinal direction becomes non-uniform and there arises a possibility that the irregularity of gloss or the hot offset of a fixed image derived from a partial temperature elevation may be generated in the heating and fixing device.
3) Further, since the heat roller system exhibits a greater heat radiation quantity at end portions than the center in a fixing nip area compared with the film heating system, it becomes impossible to make a heat quantity applied to the recording member uniform and hence, there arise technical problems that the insufficient heating or the failure of fixing is brought about or toners are offset to a film at the center contrary to the film heating system.
4) Further, when sheets which constitute recording members and have a width narrower than a width of a heating area are made to pass the heating area, the heat of an area where the sheets do not pass is not consumed, and hence there also arises a technical problem that the temperature of such an area becomes higher than the temperature of the other areas.
As related arts which solve such technical problems (tasks on non-uniformity of temperature), followings are named.
The Japanese Patent Laid-open No. 30126/1996 discloses a solution in which, in an electromagnetic induction heating device, by arranging a member having a favorable heat conductivity over a heating portion in the longitudinal direction for heating an object to be heated, the temperature distribution is corrected by the dissipation of heat.
The Japanese Patent Laid-open No. 179647/1996 discloses a solution in which, by setting a winding diameter of an exciting coil arranged in the inside of a fixing roller at both longitudinal end portions thereof greater than the winding diameter of the exciting coil at a central portion thereof, the generation of heat at the both end portions of the roller is increased to provide a uniform temperature distribution.
The Japanese Patent Laid-open No. 26719/1997 discloses a solution in which, with respect to a distance between an exciting coil and an electromagnetic induction heat generating layer inside a fixing roller, by narrowing the distance at both end portions than the distance at a central portion, the absorption of a magnetic flux at both end portions is increased so that a heat value is increased whereby the sharp lowering of temperature at the end portions is corrected.
The Japanese Patent Laid-open No. 10901/1988 discloses a solution in which a core of an exciting coil is provided with the plural wiring corresponding to sizes of recording members and the generation of heat corresponding to the size of a passing recording member can be selected thus making the temperature uniform.
The Japanese Patent Laid-open No. 31379/1998 discloses a solution in which, in a low-frequency induction heating system, by making the resistance at both end portions of a fixing roller smaller than the resistance at a central portion of the fixing roller, the generation of heat at the end portions is increased so that the temperature distribution of an exciting roller can be made uniform.
The Japanese Patent Laid-open No. 106207/1997 discloses a solution in which the plural cores are arranged in the inside of a fixing roller and exciting coils are respectively wound around the cores and a parallel connection and a series connection are suitably combined as a connection structure of each exciting coil so as to make the temperature distribution of the fixing roller approximately uniform.
The Japanese Patent Laid-open No. 167982/1999 discloses a solution in which, at both end portions of an electromagnetic induction heat generating member (an object to be heated), an exciting coil is arranged in an inclined manner to an advancing direction of the exciting coil so that a heat value is increased thus making the temperature uniform.
The Japanese Patent Laid-open No. 202652/1999 discloses a solution in which a shape of a core of an exciting coil is formed in a tapered shape at both end portions of the core so that a magnetic flux absorbed at both end portions can be increased thus making the temperature distribution uniform.
The Japanese Patent Laid-open No. 39796/2000 discloses a solution in which temperature can be made uniform using the self temperature control characteristics of an object to be heated which makes use of phenomenon that the generation of heat of the object to be heated is decreased in the vicinity of a Curie point.
In this manner, although many proposals have been made in the past with respect to ideas to make the temperature distribution of the object to be heated uniform, these proposals respectively have advantages and disadvantages (examples of disadvantages: poor thermal efficiency, complicate constitution and the like) and hence, it has been practically difficult to adopt these proposals.
Further, although all of these related arts aim at making the temperature distribution of an object to be heated uniform, no consideration have been paid to an idea to freely obtain the distribution of heat generation which matches an object.
The present invention has been made in view of the above circumstances and provides an electromagnetic induction heating device which can freely adjust the heat generation distribution of an object to be heated and can easily obtain the heat generation distribution which matches a purpose and an image recording device which uses such an electromagnetic induction heating device.
According to the present invention, there is provided an electromagnetic induction heating device which has an object to be heated having at least an electromagnetic induction heat generating layer, a magnetic field generating unit which is arranged facing the electromagnetic induction heat generating layer of the object to be heated and includes an exciting coil which generates a magnetic flux penetrating the electromagnetic induction generating layer, and a magnetic flux adjusting member which is made to be interlinked with a portion of the magnetic flux of the exciting coil to generate an electromagnetic induction action so that the magnetic flux acting on the electromagnetic induction heat generating layer is changed is disposed in the vicinity of the exciting coil.